The present invention relates to a braking device for a motor saw, including a rotatable brake drum, a brake band surrounding the brake drum and actuatable by a spring which is adapted, when in an activated position, to stretch the brake band around the brake drum, and a toggle joint mechanism adapted to release the brake band from the drum against the action of the spring and to latch the braking device in a working position in which the brake band is released, the toggle joint mechanism being actuatable by a control means for adjusting the position of the brake band relative to the brake drum.
Braking devices of this kind are used for preventing injury of the operator by the cutting tool, usually a saw chain, due to a sudden kickback of the saw. When such a kickback occurs, the control means is actuated whereby the brake band is applied to the brake drum and the saw chain is stopped. In order to enable continued operation of the saw, the braking device must then be reset to its released position which is performed by the control means and against the action of the spring.
The saw chain must be braked in a very short time which results in a heavy load on the brake band. The heavy load on the brake band, in combination with the failure to replace the brake band when worn, may, in rare occasions, lead to rupture or severing of the brake band. Since the brake band is enclosed or concealed within the saw housing, rupture of the brake band cannot be easily observed, and the operator may, therefore, reset the control means to the operational position and continue using the saw while mistakenly believing that the brake is functioning normally. It is easily realized that this implies an obvious risk of injury at the next occurrence of a kickback, since the braking device will then not function to stop the saw chain.